Process for removing trace amounts of water and sec-butyl mercaptan from coker propylene

Abstract

This invention discloses a process for removing trace amounts of water and sec-butanethiol from coking propylene, belonging to the field of petrochemical technology. The technical solution is as follows: Coking propylene material enters the distillation column from the lower part of the reaction section. The coking propylene material passes through the upper rectification section of the distillation column, where stainless steel packing separates propylene, water, and sec-butanethiol. The middle section of the distillation column is the reaction section, where carbonyl sulfide is converted into hydrogen sulfide and carbon dioxide through a carbonyl sulfide hydrolysis reaction. The lower section of the distillation column is the stripping section, which is also packed with stainless steel packing to separate propylene, water, and sec-butanethiol. At the top of the column, propylene after the removal of water, sec-butanethiol, and carbonyl sulfide hydrolysis is obtained; at the bottom, two layers of propylene and water are obtained. The aqueous phase is periodically discharged. This invention has a simple process flow, simultaneously completing dehydration, sec-butanethiol removal, and carbonyl sulfide conversion, regardless of the concentration of impurities in the coking propylene. It can be adapted to different raw materials from different manufacturers, facilitating centralized processing of coking propylene, increasing production volume, and reducing costs.

Description

Technical Field

[0001] This invention relates to the field of petrochemical technology, specifically to a process for removing trace amounts of water and sec-butanethiol from coking propylene. Background Technology

[0002] Traditional coking propylene contains impurities such as 250-270 ppm water, 1-4 ppm sec-butanethiol, and 1-6 ppm carbonyl sulfide. Due to these impurities, coking propylene cannot be used for polymer-grade or chemical-grade propylene. It needs to be properly treated to remove these impurities before it can be used as a raw material for butyraldehyde or polypropylene to increase the added value of the products.

[0003] Traditional processes for removing trace amounts of water, sec-butanethiol, and carbonyl sulfide from propylene generally employ adsorption with several reactors connected in series.

[0004] (1) A carbonyl sulfur hydrolysis catalyst is loaded into the first reactor to carry out the hydrolysis reaction of carbonyl sulfur with water, so that carbonyl sulfur is converted into hydrogen sulfide and carbon dioxide;

[0005] (2) A dehydrating agent is loaded into the second reactor to remove trace amounts of water from the propylene, and at the same time, some sec-butanethiol is inevitably removed.

[0006] (3) The adsorbent for removing sec-butanethiol is loaded into the third reactor to remove sec-butanethiol.

[0007] Because coking propylene contains numerous impurities, including trace amounts of water, sec-butanethiol, and carbonyl sulfide, as well as both low-boiling-point carbonyl sulfide and high-boiling-point sec-butanethiol and water, the simultaneous removal or conversion of these impurities has become a major challenge for technicians. Traditional processes are complex, prone to adsorbent saturation, have unstable operation, high energy consumption, and involve a complicated process flow of adsorption saturation, shutdown, regeneration, and tail gas treatment.

[0008] The adsorption process is highly dependent on the concentration of impurities in propylene and has poor adaptability. If the concentration of impurities such as water and thiols changes, the process conditions for adsorption also change. The water content in the adsorbed propylene may exceed 10 ppm, failing to meet the requirements for polymer-grade propylene. Furthermore, the sec-butanethiol content in the adsorbed propylene easily exceeds the standard, failing to meet the quality requirements for chemically-treated propylene. In summary, traditional adsorption processes suffer from drawbacks such as incomplete impurity adsorption, complex process flow, high energy consumption, and poor adaptability to the concentration of impurities in the raw materials. Summary of the Invention

[0009] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies and provide a novel catalytic distillation process for removing trace amounts of carbonyl sulfide, trace amounts of water, and sec-butanethiol from coking propylene. The resulting propylene at the top of the distillation column has a water content of less than 1 ppm and a sec-butanethiol content of 0.001 ppm. Simultaneously, a hydrolysis reaction of carbonyl sulfide occurs in the reaction section, increasing the added value of the product. A certain concentration of wastewater (containing trace amounts of sec-butanethiol) is discharged from the bottom of the distillation column and sent to a wastewater treatment plant for further treatment. Propylene is not discharged from the bottom of the distillation column; it serves to maintain the liquid level and temperature.

[0010] The technical solution of this invention is: a process for removing trace amounts of water and sec-butanethiol from coking propylene, comprising the following steps:

[0011] Coking propylene material containing trace amounts of water, sec-butanethiol, carbonyl sulfide, and other sulfides enters the distillation column from the lower part of the reaction section. The coking propylene material passes through the stainless steel packing in the upper rectification section of the column to separate propylene, water, and sec-butanethiol. The middle section of the distillation column is the reaction section, where carbonyl sulfide is hydrolyzed to convert it into hydrogen sulfide and carbon dioxide, which are discharged from the top of the column along with the propylene. The lower part of the distillation column is the stripping section, which is packed with stainless steel packing to separate propylene, water, and sec-butanethiol. At the top of the column, propylene after the removal of water, sec-butanethiol, and carbonyl sulfide hydrolysis is obtained. At the bottom of the column, two phases are obtained: a propylene phase and an aqueous phase. Sec-butanethiol is extracted from the propylene phase by water and enters the aqueous phase, which is discharged periodically. The aqueous phase is sent to a wastewater treatment plant for treatment.

[0012] Preferably, the mass content of the water phase at the bottom of the tower is 0.3-13%.

[0013] Preferably, the mass content of the water phase at the bottom of the tower is 1-10%.

[0014] Preferably, the stainless steel packing is used in a packed tower or a plate tower.

[0015] Preferably, the reaction section is filled with a carbonyl sulfur hydrolysis catalyst, and the catalyst filling structure is an MP-Ⅲ type filling structure.

[0016] Preferably, the carbonyl sulfur hydrolysis catalyst in the reaction section is T909.

[0017] Preferably, in the distillation column, the pressure P = 1.5-2.0 MPa and the top temperature T 顶 =35-45℃, tower bottom temperature T 釜 =38-48℃, reflux ratio R=0.1-0.5, number of trays N=15 (pieces), N 精馏 =5 (blocks) N 反应 =5 (blocks), N 提留 =5 (blocks), volumetric space velocity Sv=1-2h-1.

[0018] Preferably, the conversion rate of carbonyl sulfur hydrolysis reaction is 100%, the water content in the propylene at the top of the column is ≤1ppm, the water removal rate is ≥99.9%, the sec-butanethiol content in the propylene at the top of the column is 0.001ppm, the sec-butanethiol removal rate is ≥99.9%, and the propylene output from the top of the column is ≥99.9%.

[0019] Process Principle: Separation is achieved by utilizing the significant boiling point difference between propylene, water, and sec-butanethiol, preventing the formation of an azeotrope. Simultaneously, carbonyl sulfide undergoes hydrolysis during the reaction. Propylene and water are immiscible, while sec-butanethiol is only slightly soluble in water. When the water content in the bottoms increases to a certain level, propylene and water phases easily separate. sec-butanethiol is readily extracted from the propylene phase and vice versa in the bottoms, achieving automatic separation. Due to the near immiscibility and significant density difference between the propylene and water phases, automatic stratification is achieved. A single distillation column simultaneously performs separation, hydrolysis, and extraction functions, conducting the following reactions concurrently:

[0020] (1) Hydrolysis reaction of carbonyl sulfide;

[0021] (2) Dehydration;

[0022] (3) Removal of sec-butanethiol;

[0023] (4) sec-butyritin is extracted from the propylene phase into the aqueous phase by water, thus achieving separation from the propylene phase. The propylene phase and the aqueous phase achieve automatic separation by relying on the density difference and immiscibility.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] 1. The process flow of this invention is simple and easy to implement, eliminating the problems of adsorbent regeneration and waste gas treatment; it removes impurities cleanly and thoroughly; the process is stable and adaptable to impurities in the raw materials; it completes the hydrolysis reaction of carbonyl sulfide simultaneously with separation, saving industrial equipment and reducing energy consumption; the water content in the propylene at the top of the tower after treatment is less than 1 ppm, and the sec-butanethiol content is 0.001 ppm, meeting the standard for polymer-grade propylene and increasing the added value of the product. The water content in the bottom material is 0.3-13% (m), achieving automatic stratification with the propylene phase. sec-butanethiol is easily separated from the propylene phase by water through extraction and transferred to the aqueous phase, realizing the separation of impurity components from the propylene phase. The aqueous phase discharged from the bottom of the tower is sent to a wastewater treatment plant for further treatment.

[0026] 2. The process flow of this invention is simple. A single catalytic distillation column simultaneously completes dehydration, removal of sec-butanethiol, and carbonyl sulfide conversion. This process is independent of the concentration of impurities in the coking propylene, allowing it to adapt to different raw materials from different manufacturers. It facilitates centralized processing of coking propylene, increasing production volume and reducing costs. Due to the low reflux ratio and low temperature, low-temperature energy can be effectively utilized, resulting in low energy consumption. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the present invention. Detailed Implementation

[0028] Example 1

[0029] like Figure 1 As shown, this embodiment provides a process for removing trace amounts of water and sec-butanethiol from coking propylene, specifically as follows: The coking propylene contains 260 ppm of water, 2 ppm of sec-butanethiol, 3 ppm of carbonyl sulfide, and other impurities. These impurities enter the distillation column from the lower part of the reaction section, under conditions of P = 1.5 MPa and T... 顶 =35℃, T 釜 =39℃, R=0.2, N=10 (pieces), N 反应 =5 (blocks), Sv=1.2h -1 Under the specified process conditions, the catalytic distillation column adopts an MP-Ⅲ type packing structure, the carbonyl sulfur hydrolysis catalyst is T909, and when the water content in the bottom of the column is 4%, the carbonyl sulfur content in the propylene at the top of the column is 0 ppm, the water content is 0.5 ppm, and sec-butanethiol is not detected. Two layers of propylene and water are obtained at the bottom of the column. sec-butanethiol is extracted from the propylene phase by water and enters the aqueous phase, which is discharged with the aqueous phase and sent to the wastewater treatment plant for treatment.

[0030] Example 2

[0031] Coking propylene contains impurities such as 255 ppm water, 4 ppm sec-butanethiol, and 5 ppm carbonyl sulfide. At P=1.7 MPa and T... 顶 =39℃, T 釜 =41℃, R=0.3, number of trays N=15 (pieces), N 精馏 =5 (blocks), N 反应 =5 (blocks), N 提留 =5 (blocks), Sv=1.5h -1 Under the specified process conditions, the catalytic distillation column adopts an MP-Ⅲ type packing structure, the carbonyl sulfur hydrolysis catalyst is T909, and when the water content in the bottom of the column is 6%, the carbonyl sulfur content in the propylene at the top of the column is 0 ppm, the water content is 0.7 ppm, and sec-butanethiol is not detected. Two layers of propylene and water are obtained at the bottom of the column. sec-butanethiol is extracted from the propylene phase by water and enters the aqueous phase, which is discharged with the aqueous phase and sent to the wastewater treatment plant for treatment.

[0032] Example 3

[0033] The coking propylene contains impurities such as 268 ppm water, 3 ppm sec-butanethiol, and 4 ppm carbonyl sulfide. At P=2.0 MPa and T... 顶 =44℃, T 釜 =37℃, R=0.4, number of trays N=15 (pieces), N精馏 =5 (blocks), N 反应 =5 (blocks), N 提留 =5 (blocks), Sv=2.0h -1 Under the specified process conditions, the catalytic distillation column adopts an MP-Ⅲ type packing structure, the carbonyl sulfur hydrolysis catalyst is T909, and when the water content in the bottom of the column is 9%, the carbonyl sulfur content in the propylene at the top of the column is 0 ppm, the water content is 0.6 ppm, and sec-butanethiol is not detected. Two layers of propylene and water are obtained at the bottom of the column. sec-butanethiol is extracted from the propylene phase by water and enters the aqueous phase, which is discharged with the aqueous phase and sent to the wastewater treatment plant for treatment.

[0034] Comparative Example 1

[0035] The coking propylene contains impurities such as 268 ppm water, 3 ppm sec-butanethiol, and 4 ppm carbonyl sulfide. At P=2.0 MPa and T... 顶 =44℃, T 釜 =37℃, R=0.25, number of trays N=15 (pieces), N 精馏 =5 (blocks), N 反应 =5 (blocks), N 提留 =5 (blocks), Sv=2.0h -1 Under the specified process conditions, the catalytic distillation column adopts an MP-Ⅲ type packing structure, the carbonyl sulfur hydrolysis catalyst is T909, the water content in the bottom of the column is 0.05%, the bottom material does not separate into layers, and the water layer cannot be discharged. The carbonyl sulfur content in the propylene at the top of the column is 0 ppm, the water content is 0.6 ppm, and sec-butanethiol is not detected.

[0036] Comparative Example 2

[0037] The coking propylene contains impurities such as 268 ppm water, 3 ppm sec-butanethiol, and 4 ppm carbonyl sulfide. At P=2.0 MPa and T... 顶 =44℃, T 釜 =37℃, R=0.35, number of trays N=15 (pieces), N 精馏 =5 (blocks), N 反应 =5 (blocks), N 提留 =5 (blocks). Sv=2.0h -1 Under the specified process conditions, the catalytic distillation column adopts an MP-Ⅲ type packing structure, the carbonyl sulfur hydrolysis catalyst is T909, and when the water content in the bottom of the column is 0.11%, the bottom material does not separate into layers and the water layer cannot be discharged. The carbonyl sulfur content in the propylene at the top of the column is 0 ppm, the water content is 0.5 ppm, and sec-butanethiol is not detected.

[0038] This invention features a simple and easy-to-implement process, eliminating the need for adsorbent regeneration and waste gas treatment. It removes impurities thoroughly and cleanly, ensuring process stability and adaptability to various impurities in the raw materials. Simultaneously, it completes the hydrolysis of carbonyl sulfide during separation, saving industrial equipment and reducing energy consumption. The treated propylene at the top of the column has a water content of less than 1 ppm and sec-butanethiol content of 0.001 ppm, meeting the standards for polymer-grade propylene and increasing product added value. The bottom material has a water content of 0.3-13% (m), achieving automatic stratification with the propylene phase. sec-butanethiol is easily separated from the propylene phase by water through extraction, transferring to the aqueous phase, thus separating impurity components from the propylene phase. The aqueous phase discharged from the bottom of the column is sent to a wastewater treatment plant. This invention's process is simple, with a single catalytic distillation column simultaneously completing dehydration, sec-butanethiol removal, and carbonyl sulfide conversion, independent of the concentration of impurities in the coking propylene. It can adapt to different raw materials from different manufacturers, facilitating centralized processing of coking propylene, increasing production volume, and reducing costs. Due to the low reflux ratio and low temperature, low-temperature energy can be effectively utilized, resulting in low energy consumption.

[0039] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the invention should also be covered within the protection scope of the invention. Therefore, the protection scope of the invention should be determined by the scope of the claims.

Claims

1. A process for removing trace amounts of water and sec-butanethiol from coking propylene, characterized in that, Including the following processes: Coking propylene material containing trace amounts of water, sec-butanethiol, carbonyl sulfide, and other sulfides enters the distillation column from the lower part of the reaction section. The coking propylene material passes through the stainless steel packing in the upper rectification section of the column to separate propylene, water, and sec-butanethiol. The middle section of the distillation column is the reaction section, where carbonyl sulfide is hydrolyzed to convert it into hydrogen sulfide and carbon dioxide, which are discharged from the top of the column. The lower part of the distillation column is the stripping section, which is also packed with stainless steel packing to separate propylene, water, and sec-butanethiol. At the top of the column, propylene after the removal of water, sec-butanethiol, and carbonyl sulfide hydrolysis is obtained. At the bottom of the column, two layers of propylene and water are obtained. Sec-butanethiol is extracted from the propylene phase by water and enters the aqueous phase, which is discharged with the aqueous phase and sent to a wastewater treatment plant for further treatment. The water content at the bottom of the tower is 0.3-13% by mass; In a distillation column, the pressure P = 1.5-2.0 MPa and the top temperature T 顶 =35-45℃, tower bottom temperature T 釜 =38-48℃, reflux ratio R=0.1-0.5, number of trays N=15 (pieces), N 精馏 =5 (blocks), N 反应 =5 (blocks), N 提馏 =5 (blocks), volumetric space velocity Sv=1-2h -1 .

2. The process for removing trace amounts of water and sec-butanethiol from coking propylene as described in claim 1, characterized in that: The water content at the bottom of the tower is 1-10%.

3. The process for removing trace amounts of water and sec-butanethiol from coking propylene as described in claim 1, characterized in that: The reaction section is filled with a carbonyl sulfur hydrolysis catalyst, and the catalyst packing structure is an MP-Ⅲ type packing structure.

4. The process for removing trace amounts of water and sec-butanethiol from coking propylene as described in claim 3, characterized in that: The catalyst for the carbonyl sulfur hydrolysis in the reaction section is T909.

5. The process for removing trace amounts of water and sec-butanethiol from coking propylene as described in claim 1, characterized in that: The conversion rate of carbonyl sulfur hydrolysis reaction is 100%, the water content in the propylene at the top of the column is ≤1ppm, and the water removal rate is ≥99.9%; the sec-butanethiol content in the propylene at the top of the column is 0.001ppm, and the sec-butanethiol removal rate is ≥99.9%; the propylene output from the top of the column is ≥99.9%.

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